An etchant placed on a hard tissue will dissolve the substrate in such a way as to allow for good mechanical retention of a cured adhesive or other coating which is applied subsequent to the etching treatment. In the dental art, the use of a dental etchant is generally necessary to obtain optimal bonding of a restorative or other material to dentin or enamel. To attain proper etching at the desired location on the hard tissue, it is desirable that the etchant be controllable and slow to flow away from it target site. Thus a high viscosity etchant in the oral environment would be quite useful.
Currently available etchants are provided in seemingly extreme viscosity states. That is, there exist compositions that have very low viscosities as well as compositions that are highly thickened and therefore possess high viscosity. Those with low viscosities are difficult to control and have tendencies to flow away from the target site once it is applied. Compositions with high viscosities are difficult to extrude through a small orifice.
Certain etchant compositions may use thickeners such as fumed silica and polyvinyl alcohols. Problems encountered in using these thickeners include aging, which results in non-homogenous gels which make handling difficult, and shear thinning, which reduces the viscosity of a gel when extruded through an orifice and thinning at elevated temperatures. Thinning can result in a material that drips onto soft tissue causing irritation and damage to the tissue.